1. Field of the Invention
Disclosed herein are water-based drilling mud compositions containing volcanic ash and related methods.
2. Description of the Related Art
Traditionally bentonite or extended bentonite is used as a drilling mud additive in the oil and gas, geothermal, and water well drilling industries for hole cleaning, cuttings suspension, formation support, and the like while drilling. The bentonite clays are known to swell significantly when contacted with water and accordingly are used to produce viscous properties and fluid loss control in water-based mud systems. The bentonite materials are generally dispersed or suspended in fresh water by mixing it properly or occasionally in salt water if pre-hydrated with fresh water before being added to salt water. Ingredients such as gelling or thickening agents or fluid loss additives are sometimes incorporated into the bentonite mud composition to enhance its viscous, gelling, and fluid loss properties.
The bentonite clay that is used in many prior art applications could be the high swelling or the poorly-swelling types, depending on the availability of the material. However, enhancement or extension of poor quality bentonite is usually done using some polymers known as bentonite extenders. Due to high swelling properties of bentonites, good viscosity building capability with fresh water, ease of formulation and easy availability of bentonite material in the global market, environment friendliness of bentonites and bentonite-based muds, it is a common drilling mud that is widely used as in spud and surface hole drilling mud systems. Bentonite mud is also used to drill the non-reservoir section of the surface hole ranging from a couple of hundred feet to more than a thousand feet.
Conventional bentonite mud, though widely used for surface hole drilling, has serious technical limitations due to poor tolerance to monovalent and divalent salts, undesirable mud solids, cement contamination, pH changes, and temperature changes above 100° C. This type of mud system also has strong interactions with subsurface formations such as anhydrite, evaporite, salt diapirs, clay rich formations, reactive shale, marls, and the like. As salt cannot be used to inhibit the reactive fresh water phase of the bentonite mud, it creates serious borehole problems in drilling evaporite, anhydrite, and reactive shales that are frequently encountered in many fields. Due to the high dissolution capacity of fresh water used in bentonite mud formulations, it often leads to hole enlargement and loss of circulation problems while drilling shales, evaporites, and anhydrites. The bentonite mud triggered borehole problems can lead to the set up of an unplanned casing string with a significant increase in total well costs and may also lead to a poor cementation job leading to a remedial action for a correction.
However, due to serious technical limitations of the bentonite muds, they are ineffective in drilling evaporite, anhydrite, clay rich, and salty formations in many fields. Other problems that exist when using prior art bentonite mud systems can include poor salt, saline water, solids, and cement tolerance, along with high sensitivity to pH and temperature changes. Many prior art bentonite mud are not tolerant to monovalent and divalent salts; have poor thermal and chemical stability; have little to no cement and poor solids tolerance; and are incompatible to drill anhydrite, evaporite, clays, marls, reactive shale, salt diapirs, and the like.
A need exists for mud compositions that have monovalent and divalent salt tolerance, cement tolerance, high chemical stability in a wide pH range, good thermal stability to prevent thermally induced thickening, good mudcake building properties, low fluid loss potential, and the like. It would be advantageous for the mud system to also have the potential to maintain a good borehole profile in drilling evaporite, anhydrite, and reactive shale formations to overcome the drilling challenges that are encountered while drilling the top sections of a wellbore and also the total non-reservoir section of a borehole.